The present invention relates to a method of shaping glass sheets. More specifically, the present invention relates to a method of shaping glass sheets by roll forming such that undesired curvature may be selectively minimized/eliminated from desired portions of the glass sheet.
In a roll forming operation, glass sheets suitable for use as, for example, vehicle windows are conventionally heated to temperature suitable for shaping and are conveyed by a conveying system into a first roll shaping zone, where they are conveyed between upper and lower sets of rotating shaping rolls having a first shaping configuration. Each set of upper and lower shaping rolls have complementary shapes so as to allow a glass sheet to pass therebetween, and to take the cumulative shape of the entire set of upper and lower shaping rolls, while still being susceptible to further alterations in shape. In general, shaping in the first roll shaping zone is preferably transverse to the direction of travel of the glass sheet.
It is advantageous to transport the heated glass sheets through the roll shaping zone at as high a velocity as practicable to reduce cycle time, and to maintain the glass sheet at a temperature sufficient to allow additional shaping in, for example, an inclined second roll shaping zone. Such additional glass shaping is preferably accomplished by the glass sheet being transported from the horizontal first roll shaping zone, up the slope of the inclined second roll shaping zone.
Bending a heated glass sheet by roll forming is known in the patent literature. Examples include:
U.S. Pat. No. 3,545,951 describes a plurality of arcuately curved rods mounted for rotation each about its own chordal axis. The axes are said to be coplanar, parallel and spaced, and the rods are said to be interconnected for pivoting in unison each about its own axis, from a first position, wherein they are said to be coplanar in a common plane through all axes, to a second position wherein they are said to conjointly define a curved surface whose curvature is variable in dependence upon the angle of rotation of the rods. Sheets said to be in bendable form are moved onto the rods in the first position. The rods are then pivoted to the second position and shaping means complementary to the curved surface defined by the rods are pressed down onto the sheet to conform it to the rods, while the sheet moves continuously, and after shaping, passes to a cooling and tempering chamber or other processing procedure.
U.S. Pat. No. 3,831,239 describes an improved form of corrugated tube intended to facilitate the rotation of the corrugated tubes about curves rods. The inside diameter of the flexible tube is made larger than the diameter of the current rod. A plurality of rings is disposed on the inside of the tube, each ring being located between two adjacent corrugations, the rings being at suitable intervals along the length of the tube. These rings rotate with the tube around the rod. Due to the presence of the rings (sometimes referred to as bearing rings), the flexible tube does not come into contact with the curved rod. The portions of the tube suspended between adjacent bearing rings are capable of sustaining sufficient stress from the sheets without collapsing onto the rod, and are thus capable, in combination with the rods, of imposing the desired shape on the glass sheets.
U.S. Pat. No. 4,054,437 describes a sheet to be curved, such as glass at a softening temperature, being advanced on a fixed curved bed formed by a series of curved rods having different angles of inclination to form an ascending convex bed with an increasing curvature profile. The sheet is thus gradually raised and simultaneously curved by sagging of the edges thereof. The curved rods are said to have aligned end sections mounted in the same horizontal plane and the inclinations progressively increase. The bed is followed by a bed of constant curvature profile formed by curved rods having the same inclination. Means are said to be provided for independently adjusting the inclination of each rod. Particular ranges of spacing and rate of advance are said to be given.
U.S. Pat. No. 4,054,438 describes a roll forming system similar to U.S. Pat. No. 4,054,437, except that the assemblage of rods are fixed in orientations throughout the roll forming cycle, thus not requiring the mechanical and electrical equipment necessary to raise and lower the assemblage of rods during each bending cycle. Also, if the orientation of the rods is altered to make a different part, the roller and beam system of the invention allows the rods to be repositioned as a unit, rather than individually.
U.S. Pat. No. 4,123,246 describes shaped solid members such as successive rotating shaping rolls of predetermined contour of a uniform cylindrical or curved configuration which engage a heat-softened glass sheet along an arcuate longitudinal path of substantially constant radius of curvature along forming and quenching conveyors to impart a desired longitudinal component of curvature to the glass and to convey the shaped glass past cool blasts that harden the glass surfaces. The arcuate path is said to be arranged in such a manner that its upward slope at its downstream end is said to be limited to one at which glass sheets move forward toward the cooling conveyor without slipping. A set of at least three special quench rolls forms an upwardly sloped transition conveyor section of constant maximum slope that replaces the downstream portion of the arcuate path where the upward slope would increase to a slope where slippage would take place. The special transition quench rolls are located downstream of the location where blasts of tempering fluid applied at the quenching section have hardened the major glass sheet surfaces sufficiently to, desirably, avoid their distortion by engagement with the rotating special transition quench rolls.
U.S. Pat. No. 4,292,065 describes a method and apparatus for bending sheets in the plastic state, such as sheets of glass at their softening temperature in two directions. The apparatus comprises a first bed of arcuate rods which can be positioned to impart a transverse curvature to the sheet and a second bed of arcuate rods which can be positioned to impart a longitudinal curvature to the sheet. Advantageously, the bending is performed in a heated enclosure at a temperature at least equal to that at which the sheet is later tempered.
U.S. Pat. No. 4,820,327 describes bending a heated glass plate by moving it over a bed of rollers defining a path curved along the direction of movement of the glass plate so as to define an upwardly facing concavity. The glass plate moves with a speed of at least 10 cm/sec and is curved by the bed without contact from above. The glass plate is subsequently tempered.